The spread of HIV has slowed in SA in the past five years, with HIV incidence falling by almost half.

But researchers are worried that the gains are largely due to interventions such as the provision of antiretroviral (ARV) treatment and male circumcision, rather than because people are changing their behaviour to reduce their risk of transmission.

The findings are contained in the latest South African National HIV Prevalence, Incidence and Communication Survey, released on Tuesday, and raise questions about whether the government may have expanded its HIV treatment programme at the expense of prevention efforts.

The survey is the fifth in a series that has been conducted since 2002, and was led by scientists at the Human Sciences Research Council (HSRC). It was conducted between January and December 2017 and included interviews with more than 33,000 people, of whom 24,000 agreed to take an HIV test.

It found the HIV incidence rate almost halved between 2012 and 2017, dropping from 0.85% to 0.48%, as the annual number of new infections fell from 469,000 to 231,000. The proportion of men who were circumcised rose from 18.6% to 30.8% over the five year period, while the number of HIV-positive patients on treatment rose from 2.4-million to 4.4-million.

However, consistent condom use was low, early sexual debut increased (particularly among men), and more than a third of young women were in relationships with older men.

"We’ve made progress with biomedical interventions, but unfortunately we are not making progress with behavioural change," said one of the study’s principal investigators, HSRC researcher Mpumi Zungu. "Changing attitudes is complex — a lot of work still has to be done. We need to remind people that HIV is still infectious and that you are at risk if you are not using condoms," she said.

Young men and women aged between 15 years and 24 years reported the same degree of condom use at their last sexual encounter as they had in 2012, at 49.8% for women and 67.5% for men. However, these figures are markedly lower than those reported in the 2008 survey, which found 66.5% of young women, and 85.2% of young men had used condoms the last time they had sex.

The survey also showed that more South Africans were starting to have sex when they were young teenagers, increasing their risk of HIV: the proportion of young women who reported their age of sexual debut as being younger than 15 years rose from 7.6% to 19.5% between 2008 and 2017, while the figure rose in young men, from 11.3% to 19.5% during that time.

Zungu said SA had made progress towards the UN’s 90-90-90 goals, which aim to increase to 90% the proportion of people who know they have HIV, are on treatment and have a suppressed viral load, to eliminate the global epidemic by 2030. The survey found 85% of people living with HIV aged between 15 years and 64 years knew their status, 71% of them were on treatment, and 86% of those taking ARVs had a suppressed viral load.

The survey found that about 7.9-million people were living with HIV in 2017, equivalent to 14% of the population.

In line with previous research, the survey found young women aged between 15 years and 24 years were at particularly high risk of HIV infection, with an incidence rate triple that of their male peers.